1. Field of the Invention
The invention relates to a process and device for applying a liquid or paste-like medium onto a traveling material web made of paper or cardboard.
2. Description of Background Information
The inventors regard German Patent DE 194 23 48 as the most closely related prior art. As shown in FIG. 1 of this document, a fibrous suspension is deposited on a base (e.g., lower) endless wire or screen 3 by means of a headbox 1. A set of drainage elements 2 are disposed on the side of the wire or screen 3 opposite the side on which the fibrous suspension is deposited (e.g., on the inner side of the wire). A fibrous web 8 is formed along the lower wire or screen 3.
After the initial drainage zone, a second endless wire or screen 10 is arranged on the opposing (e.g., upper) side of the fibrous web 8. The base endless wire 3 has not been covered by an upper wire or screen up to this point. A second set of drainage elements 11 (suction devices) is disposed on the inner side of this second wire or screen 10, e.g., the side that does not touch the fibrous web 8. Consequently, drainage of the fibrous web 8 occurs in the opposing (e.g., upper) direction in this second region.
Opposing the second set of drainage elements 11, a set of application devices 7 (applicators) are associated with the wire surface on the underside of the base wire or screen 3. These application devices 7 introduce an application medium (additive) through the lower or base wire 3 into the fibrous web (borne on the upper side of the lower or base web 3). The drainage elements 11 (suction devices) on the inner side of the second wire 10 encourage the penetration of the application medium into the fibrous web 8. In the twin wire region (e.g., where the fibrous web is between the upper and lower endless wires or screens), essentially only drainage elements 11 are disposed on the inner side of one wire or screen 10, 3, and only application devices 7 are disposed on the inner side the other wire or screen. That is, with this arrangement, the application medium is applied to only one side of the fibrous web 8.
This structure and process are disadvantageous and use a relatively coarse wire structure. Due to the application of the application medium, the papers produced have coarse wire marks. Consequently, the resulting paper web has raised areas and recesses in the web that reduce the quality of the paper.